Presently, the state-of-the-art in the railroad and/or mass and rapid transit industry for detecting broken down or deteriorated insulated joints and audio frequency (AF) track circuits is not always very reassuring. In the past, the various methods of broken down insulated joint detection involved elaborate schemes in order to prevent false call-on of a train; a false call-on referring to the situation where a later train, normally prevented from entering a previously-occupied block, receives a cab signal to proceed; which cab signal was intended for the earlier, first train that had initially entered the particular block at an opposite end, possibly in order to take a turnout track. Due to the broken down insulated joint, the cab signal is also erroneously transmitted through to the second train, thus falsely calling the second train onto the block initially occupied by the first train. One such elaborate broken down insulated joint detecting scheme has been to utilize a detuning effect that the different frequency transmitter causes with respect to the receiver disposed across the insulated joint and which is tuned to a frequency transmitted from the other end of the block. Thus, it would be highly desirable to provide a secure and reliable method of broken down insulated joint detection in track circuits, particularly at interlockings, where safety is of the utmost importance to prevent damaged equipment and injury to personnel. A further undesirable feature of the present-day audio frequency (AF) track circuits is the large number of carrier frequencies that are required to indicate occupancy on the discrete successive block or track sections; such large number of carrier frequencies inherently increases the potential sources of interference for the particular receiver, transmitter arrangements, due to the large number of differing frequency signals being in such close proximity to one another. In certain AF systems, there are approximately twenty bond-tuning unit combinations because eight carrier frequencies are used. This has a significant impact on the logistics in manufacturing, installation, and maintenance of previous AF track circuit systems.